The diastylid genus Holostylis Stebbing, 1912, which is characterized by the presence of an apparently uniarticulate uropodal endopod, is considered valid. A supplemental description is given for the type species, Holostylis helleri (Zimmer, 1907), and the description of H. spinicauda, a new deep-water form, is presented. The new species differs from H. helleri, the only other recognized member of the genus, by apparently lacking exopods on the female and by having its telson armed with a cluster of proximal dorsal spines. A third nominal species, Holostylis gayi (Nicolet, 1849) described from Chilean waters is considered a species incertae sedis.